1. Field of the Invention
This invention relates to a dual spark plug ignition internal combustion engine which is arranged to lower the emission level of nitrogen oxides by supplying a portion of the exhaust gases into the combustion chamber of the engine, and more particularly to a cylinder head configuration of the same engine.
2. Description of the Prior Art
It has already been proposed that the combustion chamber of an internal combustion engine is supplied with a relatively large amount of the exhaust gases of the engine to mix with the air-fuel mixture in the combustion chamber, and then the air-fuel mixture mixed with the exhaust gases is ignited with two spark plugs disposed in each combustion chamber in order to lower the emission level of nitrogen oxides (NOx) maintaining relatively stable and smooth engine running.
However, the engine arranged according to the above-described proposition now requires to achieve more stable and smooth running and accordingly requires more stable combustion carried out in the combustion chamber under the condition in which a relatively large amount of the exhaust gases is supplied to the combustion chamber. Experiments reveals that the more stable combustion is achieved by expelling the combustion gases or burnt gases existing adjacent the spark plugs, adequately cooling the the spark plugs with a stream of new air-fuel mixture supplied through the intake port of the engine. The stable combustion is further improved by the secure ignition to the air-fuel mixture due to two equivalent intensity of sparks produced by the two spark plugs under generally the same condition. In this regard, it is now required to provide an improved engine which meets the above-described various conditions for achieving the stable combustion in the combustion chamber of the engine.